As an important substitute for ammonium-free leaching, magnesium sulfate is applied as a leaching agent for the mining of ion-adsorbed REE (rare earth element) deposits. Upon deriving the equation regulating the leaching kinetics on the basis of the REE “shrinking core model” during the leaching process of magnesium sulfate, we conducted leaching experiments of natural particle-sized REE deposits by applying magnesium sulfate with concentrations of 1%, 2%, 3% and 4%. Hence, the leaching efficiencies and mass transfer rates were obtained. The results show that the hybrid control equation $\frac{\mathsf{\mu }\mathsf{\delta }}{{\mathrm{D}}_1}\mathsf{\alpha }+\frac{3\mathsf{\mu }\mathrm{r}}{2{\mathrm{D}}_2}\left[1-\frac{2}{3}{\mathsf{\alpha }-\left(1-\mathsf{\alpha }\right)}^{\frac{2}{3}}\right]=\frac{3{\mathrm{C}}_0\mathrm{M}}{\mathsf{\rho }\mathrm{r}}$ is applicable for describing the leaching process when the concentration of magnesium sulfate is 1%; when the concentrations reach 2%, 3% and 4%, the external diffusion control equation $\mathsf{\alpha }=\mathrm{k}\mathrm{t}$ is appropriate to describe the leaching processes. The leaching efficiency of REE deposits reaches over 90%, specifically, 94.65%, 97.24% and 97.98%, when the concentration of magnesium sulfate is 2%, 3% and 4%, respectively. The maximum mass transfer rate appears when the concentration of magnesium sulfate is 4%, and the leaching time is reduced by 1.96 times compared to 1% concentration of magnesium sulfate. The results provide a favorable theoretical basis for the green and efficient extraction of ion-adsorbed REEs.

The basic principle of in situ leaching is chemical mining. The process of in situ leaching is to inject leaching solution into the ore body, and the leaching solution is spread in the pores of the mountain. The process is completed by the coupling action of the liquid seepage field and ion exchange reactions. In the production process, only one injection of liquid can be carried out in a certain stope, so it is impossible to improve the injection process and leaching effect through field practice. By simulating the in situ leaching process of rare earth ions, this paper builds the test stope true three-dimensional numerical model and simulates the leaching process of rare earth ore under the coupling of seepage control, ion exchange, and dilute material transfer in porous media. The migration rule of RE³⁺ and Mg²⁺ in stopes was analyzed to evaluate the leaching effect. It is of great significance to increase the recovery rate of rare earth ore.

During the in situ leaching process of ion-adsorption rare earths, leaching solution needs to be constantly injected to the mine slopes. As a consequence, landslides are highly likely to occur due to the increasing water level of soil mass. To solve this problem, we conducted a mechanical analysis on the rising water level after solution injection, which shed light on the mechanical principle of slope instability brought about by rising water level. With water level variation as the major factor, we established an early warning system for landslide risks on the basis of the real-time monitoring of water level. Within the system, a self-designed landslide early warning model is embedded. In addition to monitoring the water level variation in slopes, this system can be employed for real-time data processing. With the integration of early warning model algorithm, the real-time graded early warning of slope landslide risks is achieved within the mining process of ion-adsorption rare earths. By discussing the real-time monitoring method, framework of landslide early warning system, FIFC landslide early warning model, optimization method of water level, and selection of landslide-inducing factors, this research provides an effective solution to the landslide early warning within the mining process of ion-adsorption rare earth minerals. Thus, it can be employed as a favorable reference for other types of early warning systems.

In the in-situ leaching method of ionic rare earth, ion exchange reaction between rare earth ions and leaching agent ions is carried out, which allows the rare earth ions to be leached from the ore body as the leaching solution flows through the pores. This indicates that the leaching process of rare earth ions is closely related to the seepage field, ion exchange field, and ion migration process of the leaching solution. In this study, an ionic rare earth mine located in Longnan of Jiangxi Province was taken as the research object. By conducting nuclear magnetic resonance scanning on the ore samples of this mine and vectorizing the nuclear magnetic resonance images, a two-dimensional geometric model of pores was obtained. Then, COMSOL Multiphysics software was used to establish a coupled numerical model of seepage–exchange–migration of the ionic rare earth mine during the leaching process at the pore scale to study the seepage situation of leaching solution with different injection strengths and concentrations, as well as the exchange and migration process. The results show that increasing the concentration of magnesium ions can increase the difference of ion diffusion concentration, accelerate the forward exchange rate of ions, promote the forward exchange reaction, and improve the concentration gradient of rare earth ions in the leaching solution. The more significant the diffusion effect, the higher the ion migration rate, while at the same time inhibiting the reverse adsorption of rare earth ions, and accelerating the leaching efficiency of rare earth ions. In addition, increasing the strength of the injection solution allows rare earth ions to leach out of the ore body earlier, shortens the leaching cycle, and thus reduces the peak concentration of leached rare earth ions. By analyzing the effects of the strength of the injection solution and leaching concentration on ionic rare earth leaching, the influence of those two factors on engineering economy can be briefly evaluated, which can be provided as a reference for the optimization of ionic rare earth mining technology.